Cuprammonium-cellulose solution



Patented Sept. 22,1942

" UNITED STATES CUPRAMMONIUM-CELLULOSE SOLUTION Paul Henry Schlosser andKenneth Russell Gray, 1 Shelton, Wasln, assignors to BayonierIncorporated, Shelton, Wash Wife ., a corporation ot-Dela- 'No Drawing.Application August 22, 19M,

Serial N0. 353,599%

20 Claims. (01. 106-167) This invention relates tocuprammonium-cellulose solutions and has for its object the provision ofan improved method of preparing such solutions. More particularly, theinvention aims to provide an improved method of transforming cellulosicmaterials into cuprammonium-cellulose solutions remarkably free fromundissolved materials and lumps,'such as'undissolved and partlydissolved fibers, gels and undissolved copper salts. It ischaracteristic of the invention 101 that this transformation of thecellulosic material is brought about with marked economy of chemical andpower consumptions. Cuprammpmum-cellulose solutions prepared inaccordance with the invention may be employed in the manui'acture ofrayon, staple fiber, transparent films and the like.

Many of the various commercial cuprammoniumrayon processes which havebeen used in the past possess a number of disadvantages and wood pulpwas used, it was necessary to first fiufl'it up in order to put iteflectively into solution. In general, such processes did not involve apurification step by steeping in caustic soda and hence where wood pulpwas used, greater amounts of hemicellulose impurities would beintroduced into the yarn, this being liable to result in a weakerproduct. v

The history olthe development of the methods which have-heretofore beengenerally used in industry for preparing cuprammonium solutlons ofcellulose may be divided into thethree following stages:

a Stage I.-Cellulose was dissolved by the action of solutions which wereobtained by treating tions, though less, were still quite high. Anotherdisadvantage was that in the preparation of the copper hydroxide, thewashing of the slimy precipitated copper hydroxide tree from by-productsalts was diflicult.

Stage III.A considerable further improvement in the process forsimultaneously dissolving the cellulose and copper hydroxide was madewhen, instead of using prepared and purified copper hydroxide, a coppersulphate solution was mixed with the cellulose and then caustic soda wasadded to precipitate copper hydroxide intimately among the fibers. Insome cases the copper sulphate and caustic soda were first mixedtogether. In such procedures the troublesome operation of washing outby-productsodium sulphate, which was considered to hinder solution ofthe cellulose, could be replaced by a simpler operation in which thegreater part of the sodium sulphate was removed by simply pressing thecellulose-copper hydroxide mixture in a hydraulic press. 7

In discussing stages 11 and III of the prior art practices, only the-useof copper hydroxide has tion. The cellulose-copper hydroxide mixturewould then be dissolved in relatively strong ammonia. A very viscousmass would be formed and, since mixing usually required a considerabletime, the power consumption would be high.

copper, copper oxide or copper hydroxide with 40 vWhen thecuprammoniumcellulose solutions aqueous ammonia. Such processes had thedisadvantage that very large proportions of ammonia hadto be used todissolve the copper, and, in any event, it was diillcult to make concentrated solutions. Y very economical as regards the amount of copper usedon the basis of, the cellulose. Stage II.The next step was thereplacement of the ammoniacal copper oxide solution by pre- Suchprocesses were also not were obtained, filtration' often presenteddiilicul: ties due to the presence of large amounts. of undissolved andpartly dissolved cellulose fibres, and often also due to undissolvedcopper hydroxide, since it is usuallydiflicult' to dissolve copperhydroxide, completely in ammonia. Finally, in order to make thesolutions spin properly, it was; necessary to remove ammonia byevacuation because the excess of ammonia which was recipitated copperhydroxide puriiledi'm'm'admixed qulred for the preparation oi thesolution was lay-product salts by washing.- The precipitated copperhydroxide was intimately mixed with the cellulose, and then the admixedcellulose and copperhydroxide were simultaneously dissolved detrimentallater in spinning. I v

.The novel process of the invention represents v a considerable advanceover all of these previous processes. The process of the invention isexby ammonia and .rnechanical action. This was tremely economical inregard to both the copper and ammonia required, does not require heavyor complicated mixing machinery and yields excellent solutions which donot require any treatment prior to spinning other than the removal offoreign materials by a single filtration which can be readily madethrough ordinary filter cloth.

; Iii accordance with the general principles of the invention, thecellulosic material is first converted into a smooth paste by theconjoint action of ammonia and a basic copper salt, or efi'ectiveequivalents thereof. The conversion may be advantageously carried out inan aqueous medium containing the efiective equivalent of (1) a basiccopper salt within the range of 1 to 3 mols of copper hydroxide per 'molof normal copper salt and'(2) ammonia in amount equivalent to at least 4mols per'gram atom of the total copper be readily and economicallyprepared. The

characteristic features of the invention embodied in all of thesemodifications may be summarized- .theoretical conversion takes place notonly in the presence of cellulose but also' in the presence of ammonia,and under these conditions no copper hydroxide separates out, eventhough the ammonia concentration used is very low. Byproduct sodiumsulphate is present but does not interfere with the dissolving of thecellulose under the characteristic conditions of the invention.

2. During the main or intermediate mixing period, the coppermay beconsidered as present in the form of copper hydroxide, the amount ofalkali-metal hydroxide actually added to the paste need be only thatrequired for the theoretical conversion to copper hydroxide of thenormal copper salt constituent of the basic copper salt, so that inthis'treatment step all of the copper present may be theoreticallyconsidered to be in the form of copper hydroxide. The

- theoretical conversion of the basic copper salt (or effectiveequivalent thereof) to copper hydroxide takes place in the presence ofcellulose and ammonia and no copper hydroxide actually separates out,even though the amount of ammonia present is relatively low. Solution ofthe cellulose takes place rapidly upon the treatment form of an actualor hypothetical basic cop per salt having a composition ranging fromCuX-CMOH): to CuX-3Cu(OH)2 together with 4 to 6.5 (preferably 5.5 to 6)mols of ammonia,

' g per gram atom of the total copper in the basic with the alkali-metalhydroxide, and there results a cuprammonium-cellulose solutionsubstantlally free from undissolved copper salts. Any type of cellulosefiber or cellulosic material may .be used in practicing the invention,although the invention possesses features which make the use of woodpulp very practical in the preparation of cuprammoniumcellulosesolutions. The

- wood pulp may be used in either sheet or slush form.

In the following discussion, two main modifications of the invention areparticularly described as the A procedure and B procedure, respectively.The B" procedure is itself divided into three variants orsubmodifications. In these descriptions of the invention, basic coppersulphate is to be understood as representative of .any basic copper saltranging from CuX-CMQH): to CUX'3CI1(OH)2 where X is a bivalent anion(such as $04 or CO3) or two monovalent anions (such as Ch), and causticsoda (sodium hydroxide) is a representative alkali-metal hydroxide.Basic copper sulphate has been used merely for the purpose ofillustration, and it is to be understood that the sulphate anion may bereplaced by a carbonate, chloride or any other innocuous anion. By anyof these procedures improved cuprammonium-cellulose solutions of varyingcellulose concentrations may from v taking place.

copper salt and the correct amount of water, there. is very littletendency for the cellulose fibers to dissolve, and the properties of themix ture are such that mechanical stirring readily converts the mass toa very smooth'paste with the fibers completely dispersed but notappreciably dissolved. The production of the fibrous dispersion at thisstage may be carried out at any temperature low enough to preventvolatilizationof ammonia (in practice usually below +15 (3.). ing stage,however, it is important that a low temperature (+1 to 3 C.) beattained. This temperature may be attained in any suitable manner, asfor example by (a) operating during the intermediate mixing stage withsufiicient brine cooling to maintain such a low'temperature, (b)operating during the greater part of this stage at a moderately hightemperature (up to +15" 0.) but applying sufficient brine cooling towardthe end of the stage 'to obtain the low temperature, (0) addingicedirectly 'to the batch at the end of the stage thus reducing the tem--monia (1 to 2 mols) mixed with the caustic soda is suflicient toprevent any local coagulation The caustic soda addition is made whilecontinuing mechanical stirring. The added chemicals mix in rapidly andthen, remarkably enough, there is a practically flash dissolving of thecellulose fibers, solution being practically complete in severalminutes.

Dn'rArnEuDEscarPTromor A PROCEDURE In this procedure, basic coppersulphate (or At the end of the intermediate mixcarbonate etc.) in theform of a recovered sludge or a dry commercial powder is first mixedwith wood pulp and water, the pulp being thoroughly disintegrated in themixture. In practice one gram atom of copper or a little less is usedper mol (162 grams) of bone dry pulp. These basic copper salts possessimportant properties, in that (1) when pulp is disintegrated with themand a suitable quantity of water, they spread ,very smoothly over thecellulose fibers, and (2) when 4 to 6.5 mols of ammonia are then added,stirring readily converts the mixture to a smooth paste with the fiberscompletely dispersed but with taining suiilcient sodium hydroxide toconvert all the basic copper salt to copper hydroxide is added togetherwith a small amount of ammonia. In practice 1 to 2 mols of ammonia maybe used in this way, the amount not being actually critical.

tremely rapidly and completely. An important advantage of the method isthat solution starts with the fibers in an extremely well dispersedcondition. In the heretofore customary processes, using ammoniacalsolutions of copper oxide or a mixture of copper hydroxide and ammonia,there is a considerable tendency at the start for gelatinous lumps ofpulp to form which are hard to dissolve, and, due to the highviscosities of such cuprammonium solutions, high powered mixingequipment must be used to obtain the disintegration of. the lumps. Alsoin such processes, unless considerable excesses of copper and ammoniaare used, the solutions may contain considerable undissolved matter.

For clarity, it should be repeated that although the method of theinvention involves the use of basic copper sulphate (or basic coppercarbonate etc.), it is actually a copper hyroxide process, since whenall chemical additions have been made, the copper may be considered tobe present in the form of copper hydroxide. The important distinction,however, is that prior to solution o1 the cellulose, a dispersion of thefibers is first obtained in the presence of a copper salt or mixture ofsalts having an effective composi tion equivalent to a basic copper saltwithin the range oil to 3 mols of copper hydroxide per mol of normalcopper salt and in the presence of 4 to 6.5 mols of ammonia.

Attempts have been made to prepare cupranimonium-cellulose solutionsunder similar chem ical conditions but using either a paste of freshlyprecipitated copper hydroxide or'dry powdered copper hydroxide insteadoi using basic copper salts and later converting these to the hydroxideby caustic soda addition. In all cases, the solutions contained largeamounts of undissolved material, either undissolved cellulose or copperhydroxide or both and in many cases also lumps of undispersed fibers.Using pure copper hydroxide, a smooth intermediate dispersion, such asis obtained in the method of the invention, is not obtained, andmoreover, due to the low solubility of the copper hydroxide itself indilute ammonia of the concentrations contemplated by Upon this lateraddition, the fibers dissolve exthe invention, it is very difiicult tobring the copper hydroxide completely into solution.

While the A procedure gives extremely rapid solution of the celluloseunder very economical conditions, the procedurepossesses onedisadvantage in regard to the use of wood pulp of lower alpha contentwhich is overcome in the B procedure. The A procedure does not permit,purifying the pulp by a caustic soda steeping operation unless thesteeped pulp is washed free of caustic soda before being used in thecuprammonium procedure. "If the-steeped pulp'should be added withoutremoval of the caustic soda, the basic copper salt will be immediatelyconverted to copper hydroxide with loss of the specially advantageousfeatures of the invention. The B" procedure besides permitting asteeping operation possesses other advantages hereinafter pointed out.

DETAILED DESCRIPTION OF B" PROCEDURE The B procedure uses the essentialprinciples of the A" procedure in that during the intermediate (main)mixing stage, the copper can be considered to be present as a basiccopper sulphate having a composition within the range CLlSO4- Cu(OH) 2t0 CUSO4- CU.(OH) 2 together with 4 to 6.5 mols of ammonia. per gramatom of the total copper in the basic copper sulphate and alarge portionof the water to be contained' in the final (spinning) solution.

Unlike the A procedure, the B procedure does not use basic coppersulphate as an added reagent. Instead, the starting material is coppersulphate, which for convenience may be'added in the form of anammoniacal solution, copper sulphate beingquite soluble in diluteaqueous ammonia of suiflcient concentration to form the complex cuprictetrammino sulphate. In preparing the cuprammonium-cellulose solutions,a basic copper sulphate is formed merely as an intermediate theoreticalcompound which remains in solution due to the presence of ammonia andcellulose.

When using basic carbonates and basic sulphates in the A" procedure,only in the case of basic copper carbonate it is usually possible forpractical reasons to operate near the CuX-CMOH): end of the rangecomprising CuX-Cu( OH)z to CuX-3Cu(OH) 2, Basic copper sulphatesprecipitated from an aqueous solution of copper sulphate underconditions such as to give reasonably complete precipitation generallycontain 'Ou(OI-I)2 in at least as high proportion as represented byCuSO4-2.5Cu(OH)z to CuSO4-3.0Cu(OH)2, so in using basic copper sulphatein the A" procedure one is in effect practically restricted to this highcopper hydroxide portion 01' the desirable range unless some coppersulphate is added along with the basic sulphate. With the B procedure,however, since the .basic copper sulphate composition is only formed insitu, any point in the range 4 and hence to permit the purifying oi thepulp by a caustic soda steeping step and the directuse in the solutionprocess 01' the steeped pulp in the form or an alkali cellulose. I

While the complete "3 procedure may be carried out in a single mixingapparatus and as a continuous operation, there are actually threedistinct steps in the procedure, viz: (1) Initial breakdown (2)Intermediate stage and (3) Final stage. The additions oi materials forthe Initial breakdown and Intermediate .stages may be made essentiallyin three diiierent ways so as to arrive at the same Intermediate stagecomposition, but it is to be noted that in all three modifications, aswell asin the "A" procedure, the characteristically novel principles ofthe invention are utilized.

In outlining the B procedure, the particular modification (No. 1) firstconsidered is the one of most .general use, since by itcuprammoniumcellulose solutions can be made either with or without apulp steeping step.

OUTLINE OF B PROCEDURE-MODIFICATION No. 1

1. Initial breakdown Pulp is broken down to a slurry with anappropriate. quantity 01' water in the presence of a very smooth pastein which the fibres are ex- Iul in the earlier parts of the intermediatestage mixing and are indeed somewhat beneficial in that better mixing ispromoted.

In making a solution of low cellulose content (4%) no external coolingneed be used during the caustic soda amounting to 1.0 to 1.5 (usually1.0)

molar equivalents of caustic soda based on the copper to be added in thenext step. In the event of purifying the pulp by a steeping operation,most or all of the required caustic soda is contained inthe alkalicellulose. Ice may be substituted for part 01' the water or someexternal cooling may be applied. While a very low temperature is notrequired at this stage, it is usually convenient to have a moderatelylow temperature at this time (0 to +10 C.) in order to facilitate theattainment of the low temperature required at a later stage in theprocedure.

2. Intermediate stage A solution containing 1.0 to 1.06 mols of coppersulphate per mol of cellulose, based on the cellulose analysis in thecase of the use of alkali cellulose or per 162 grams of bone dry pulpinthe'case oi unsteeped pulp, together with4 to 6.5 mols of ammonia isthen added to the pulp slurry. Either part or all of the ammonia may becontained in the copper sulphate solution, or,

in other words, the added material may be either intermediate stage, butwhen the mass is entirelyfree from lumps and undispersed fibers, a largeice diluent addition is made lowering the temperature to +1 to 3 C. Withsolutions of' medium cellulose concentration it is usually mostconvenient to obtain temperature control by use of a combination ofexternal cooling and a smaller final ice addition, while with solutionsof high cellulose content. the low temperature is most practicallyattained by use of external cooling alone. While an internal iceaddition is in no case necessary, it has the advantage of reducing thetemperature very rapidly. This advantage is of particular importancewhen making cuprammonium-cellulose solutions ultra-rapidly, since insuch case the external cooling is not in action for sumcient time to bereally effective.

3. Final stage With the mass completely dispersed as a smooth paste andat a low temperature (+1 to -3 C.) stirring is continued and thenasolution added containing sufficient sodium hydroxide to make the totalsodium hydroxide addition inmols of ammonia required to give a coppertetrammino sulphate solution or even all the ammonia may be added in theprevious initial breakdown. On the other hand, :tollowing an initialbreakdown with caustic soda and water in the absence of ammonia, anammonia-free copper sulphate solution may be added, and then after aperiod of mixing the total'ammonia to be present at this stage may beadded. In this case, on addition of the copper sulphate, basic coppersulphate is precipitated throughout the fibrous mass. On the subsequentaddition of the ammonia, however, the mixture assumes the samecharacteristics as though the ammonia had been added simultaneously withthe copper.

In any event, when the caustic soda, copper salt, ammonia and cellulosehave been added in the proportions indicated,the mixture possesses theproperty of being very readily converted to cluding the prior additionequal to 2 mols per mol of copper and also containing 1 to 2 mols ofammonia to prevent local coagulation from taking place. This finaladdition mixes in rapidly, and

then there is a practically"flash dissolving of the cellulose fibers toyield the cuprammoniumcellulose solution. Solution'is practicallycomplete within a few minutes, but stirring may be continued longer,mainly for viscosity control.

With cuprammonium-cellulose solutions containing up to 5% cellulose,provided that either low viscosity pulp has been used or that theviscosity has been lowered by shredding and ageing the alkali cellulose,a suitable viscosity may be obtained without any further additions. Inthe event, however, or using normal viscosity pulps without ageing, orwhen using solutims of cellulose concentrations greater than- 5%, theviscosity may be readily lowered to the correct value by adding to thesolution small amounts of a viscosity-reducing agent such as ammoniumpersulphate.

OUTLINE or B PBOCEDUREMODIFICATION No. 2

This merely represents an inversion of the 1. Initial breakdown Pulp isbrokendown to a slurry with water con taining 1 to 1.06 mols cuprictetrammino sulphate per 162 grams of bone dry pulp. It is desirable tohave present during the later intermediate stage Actually somewhathigher temperatures (0 to +15 C.) are not harmmixing 4 to 6.5 mols ofammonia and this difference over the four mols of ammonia theoreticallyrequired by cupric te'trammino sulphate may be added to the water alongwith the cupric tetrammino sulphate. solution, or may be contained inthat solution as excess ammonia, or may be added later along with theIntermediate stage additions. As in the Initial breakdown forModification No. 1, ice may be substituted for part of the water.

2. Intermediate stage A solution containing 1.0 to 1.5 (usually 1.0)molar equivalents of sodium hydroxide based on the copper added in theprevious stage is now added. This solution may also contain some ammonia(up to 2.5 mols) perv mol of copper for the reason explained indiscussing the Initial breakdown. From this point on, all'conditions forthe Intermediate stage mixing including the required final temperatureand the methods for obtaining it are the same as for Modification 3.Final stage Same as for Modification No. 1.

OU'rnnvE OF B 'PRocEnonnMonIrroA'r1oN No. 3

This is again merely a further variation of the order of makingadditions for the Initial breakdown and Intermediate stages to arrive atthe same composition at the Intermediate stage and Final stage as inModification No. 1.

1. Initial breakdoum Pulp is broken down to a slurry with watercontaining 1 to 1.06 mols of copper sulphate per 162 grams of bonedry'pulp. As in Modification No. 1, ice may be substituted for part ofthe water. 2. Intermediate stage Final stage Same is in Modification No.l.

STEEIING PnooEpUBEs Foa PREPARING CUPRAM- MoNIUM-CELLULosE SOLUTIONS TheA procedure is essentially suitedto the use o; pulps having asufficiently high alpha content so that steeping is not required andhence all discussion of steeping procedures will refer to the Bcuprammonium-cellulose procedure. Cuprammonium-cellulose solutions canbe readily prepared by the B procedure without steeping the pulp at allaccording to the methodswhich have been outlined. With ordinary pulps;however, steeping is used in order to improve the quality of the finalproduct and forthis purpose steeping procedures have been developed togive special alkali celluloses containing only about half the proportionof alkali as in the type of alkali cellulose used in normal viscosepractice.

Satisfactory special alkali celluloses can be ad-' vantageously preparedin the. two ways described below.

In any event when the (a) Steeping by macerating in caustic sodasolution and centrifuging i A special alkali cellulose containing from 1to 1.06 mols Of sodium hydroxide per mol of cellulose can be preparedwhile giving the pulp a good alpha purification by macerating in7.45%.sodium hydroxide at 18 C. and then centrifuging. Steeping bymacerating and centrifuging is especially suited to the treatment of.wet bulk pulp. When wet pulp is used, sufficiently strong NaOH is usedto give a 7.45% sodium hydroxide solution including the water containedin the p p- While we do not wish to limit ourselves to the foregoingconcentration and temperature conditions, we have found thatconcentration and temperatures closely approximating the figuressmcified generally represent the optimum conditions, in view of certainpeculiarities involved in steeping by macerating. and centrifuging.

Firstly, the alkali celluloseis obtained in the form of clumps which donot shred up in an ordinary shredder but merely break up into fiakeylumps resembling soap flakes. Nevertheless, although the material is inthe form of lumps, if the foregoing optimum steeping conditions havebeen employed, it yields excellentcuprammonium-cellulose solutions sinceit later readily disperses at the Intermediate stage of the cuprammoniummixing. The steeping conditions are somewhat critical. With slightlylower sodium hydroxide concentrations, or higher temperatures, there isless swelling and poorer alpha purification. 0n the other hand if thesodium hydroxide concentration is raised, or the temperature lowered,

' there is considerably more swelling and a higher alpha purificationbutthe material no longer dissol'ves completely in the finalcuprammonium cellulose solution.

In this type of procedure, the alkali cellulose is practicallynon-ageing, and viscosity control is obtained by the use of anappropriate low vis-v co'sity pulp, or in the case of normal pulp, bythe addition of ammonium persulphate to the final cuprammonium-cellulosesolution. In either this or the steeping procedure described below, itis permissible to have the sodium hydroxide content of the alkalicellulose slightly lower than required since a corrective addition caneasily be made in the first stage of the cuprammoniumcelluloseprocedure.

' Using the correct conditions, steeping by macerating and centrifugingyields very'good cuprammonium-cellulose solutions, very free from vundissolved fibers and gels. It should be noted that the conditions oftemperature and sodium hydroxide concentration employedin this steepingprocedure are such that mercerization does not'occur.

(b) Steeping in a steeping press When using dry sheet pulp it is usuallymost convenient to steep the pulp in a steeping press,

concentration of about 10.0 to 10.3% and a temperature of about 17 to 190., followed by pressing the steeped sheets to a fairly low press-ratio--about 2.6 based on 94% bone dry pulp.

This procedure gives an alkali cellulose of the desiredcomposition--from 1.0 to 1.06 mols of sodium hydroxide per mol ofcellulose.

Using these conditions, a good alpha purificabe noted. Firstly, thesodium hydroxide concen- I tration of 10.0% to 10.3% is just within theregion where mercerization occurs'at 18 C. Secondly, the shredded alkalicellulose obtained by steeping in 10.0%- caustic in contrast to theother product undergoes viscosity ageing and hence viscosity lowering byammonium persulphate can be dispensed with in favor of alkali celluloseageing if desired.

When no steeping is used; the pulp is rapidly dissolved in any of theprocedures characteristic of the invention, when using only one gramatom of copper per mol of bone dry pulp. When using steeped pulps, it isadvisable to use from 1.0 to 1.06 mols of copper based on the amount ofcellulose indicated by the alkali cellulose analy-r sis. Also, inpreparing cu'prammoniunr-cellulose solutions using pulp from which thehemicelluloses have been largely removed by steeping, considerablybetter filtering solutions can be obtained if up to sucrose on the pulpis added in the initial breakdown along with the alkali cellulose.

ADVANTAGES AND UNIQUE FEATURES or 'rna CUBRAM- MONIUM PROCEDURES or THEINVENTION 1. Both the A and 13" procedures use the copper in forms inwhich it can be readily recovered for re-use. The basic copper sulphateused in the "A" procedure can readily be ob-v tained from wastedecoppering acid solutions by alkaline precipitating agents, in the formof a precipitate readily recoverable by filtration or settling. The Bprocedures use copper sulphate which is readily recoverable from spentdecoppering acid, either in the form of an aqueous or an ammoniacalsolution. The use of the copper thus in the form of a liquid reagent isadvantageous in aiding the maintenance of uniformity in preparingcuprammonium-cellulose solutions. There are also special advantages inusing the copper sulphate in the form of its ammonia complex; firstly,in the matter of facilitating the ammonia recovery as is described inthe copending application of'Schlosser, Bennett and Gray filed August27, 1940, Ser. No. 354,392, and secondly, in that it enables a simpleremoval of iron from the recovered copper.

2. Actually'both the A and B procedures can be considered copperhydroxide processes since when all additions have been made. enoughsodium hydroxide has been added to theoretically convert all the copperto copper hydroxide. An important point however, lies in the fact thatthis conversion takes place in the presence of both cellulose andammonia, and under these conditions no diflicultly soluble copperhydroxide separates out even though the ammonia concentration is verylow. By-product sodium sulphate is present but does not interfere withdissolving the cellulose under the con somewhat greasy in feel, and freefrom lumps and in which the cellulose fibers are completely and evenlydispersed throughout. With the mixture in this physical condition, if ithas not already been brought to a relatively low temperature by externalcooling, the temperature is lowered rapidly by means of an internal iceaddition. Now, while continuing stirring, sufficient sodium hydroxide totheoretically convert all copper to copper hydroxide'is added from asolution containing also one to two mols of ammonia (to prevent localcoagulation). On making this addition there is a practically flashdissolving of the fibers to yield a cuprammoniumcellulose solutionexceedingly free from undis solved and partly dissolved fibers and freefrom undissolved copper salts.

Onthe other hand, in the heretofore customary cuprammonium-celluloseprocesses, dis-' solving of the cellulose starts to take placeimmediately on adding to the cellulose an ammoniacal copper hydroxidesolution or a mixture of copper hydroxide and ammonia. Even though thecellulose may have been broken down to a slush previously, lu'mpscovered with thick gelatinous goo tend to form. This is especially thecase when wood pulp is used. Breaking up these lumps takes very goodmixing equipment, the mixing usually involves high power cost and thefinal cuprammonium-cellulose solution usually contains considerableundissolved and partly dissolved fibers unless considerable excesses ofcopper and ammonia are .used and often also contains undissolved copperhydroxide. Such undissolved material tends to clog .filters and evenafter filtering gives poor spinning solutions.

4. The procedures of the invention are ex- .tremely economical inregards to quantities of chemicals used. Moreover, neither high poweredmixing equipment nor a. prolonged stirring period is required. Due tothe fact that the main part of the mixing does not take place with thefibers in the form of a viscous solution but rather in the form of adispersion of fibers in a mixture having a very low viscosity, powercosts are very low.

5. There is no troublesome operation such as the removal of by-productsodium sulphate from a precipitated sludge of copper hydroxide as isfrequently the case in the prior art procedures. The lay-product sodiumsulphate remains present in the cuprammonium-cellulose solutionsprepared in accordance with the invention. but does not prevent thecellulose from dissolving under the conditions employed. In fact, theprocedures of the invention are not hindered by the presence ofconsiderable amounts. of additional sodium sulphate over that usually,formed in solution, which is of great practical advantage since it as areagent.

means that in the recovery of copper sulphate for re-use a completeseparationfrom sodium sulphate is not required.

6. By the B procedure, cuprammonium-cellulose solutions of from 4 to7%cellulose concentration and of any desired viscosity can be producedreadily. With the "A procedure solutions up to 10% cellulose can bereadily produced. On going from the lower to higher celluloseconcentrations by either'procedure, no relative increase in copper andammonia in proportion' to the cellulose is required. The only change isthat less water or ice is used, and, in the case of reducing oreliminating the internal ice additions, compensation for this byexternal cooling.

'1. The procedures are especially adapted to the use of wood pulp. Thewood pulp, moreover, does not have to be flufled up to a form similar tothat of loose linters but may be very readily used either in the form ofdry sheet pulp of wet bulk pulp.

8., The special pulp steeping methods developed in connection withmodification No. l of the B procedure give good alpha cellulosepurification and hence make the use of wood pulp competitive withlinters from the standpoint of yarn quality.

9. Cuprammonium-cellulose solutions prepared by the A orB procedureshave exceedingly low undissolved fiber and gel counts, show very goodfiltrations and spin readily without requiring any treatment other thana readily accomplished filtration. Due to the low ammonia content theycan be spun in a spin bath having a low caustic soda concentration (30grams per liter) without any necessity for ammonia removal treatmentsfirst.

1o. Cuprammonium-ceilulose solutions prepared in. accordance with theinvention can be filtered prior to spinning through ordinary clothfilters since they do not attack cloth at ordinary temperatures. This isnot the case with cuprammoniumwelluiose solutions prepared by oldermethods using considerable excesses oi copper and ammonia. since suchsolutions attack cloth filters. through other types oi. filters such asthrough steel wool or a metal screen with the result that the filtrationoperation is more dificult and less satisfactory.

11. Certain prior art methods of preparing cuprammonium-cellulosesolutions have used (or contemplated the use oi) basic copper sulphateThe methods of the invention, however, are definitely difi'erent fromsuch prior art methods. Firstly, as regards the 3" procedure, basiccopper sulphate is not used as a starting material (and need not even beformed on the fibers), but merely occurs at the intermediate stage as atheoretical composition in the presence 01' ammonia and cellulose. Also,in both the A and B procedure, the cellulose does not dissolve while thecopper is in the form of basic copper sulphate, but a mixture isobtained while the copper is in this state having.

such physical and chemical properties that a very smooth dispersion offibers is readily brought about by mechanical means. In the methods ofSuch solutions must be filtered about 1 gram atompf copper per'mol ofcellu-' cellulosic material without substantial solution thereof into asmooth paste by the conjoint action in an aqueous medium of theconstituents of a. basic copper salt containing about 1 gram atomot'copper per mol of cellulose and ammonia not exceeding 6.5 mols pergram atom of copper, and treating the resulting paste at a temperaturearound 0 C. with an alkali-metal hydroxide in amount suflicient for thetheoretical conversion of the aforesaid basic copper salt to copperhydroxide. x

2. The method of preparing a cuprammoniumcellulose solution whichcomprises converting vcellulosic material without substantial solutionthereof into a. smooth paste by the conioint actionin an aqueous mediumof the constituents of a basic copper salt containing about 1 gram atomof copper per mol of cellulose and ammonia not exceeding 6.5 mols pergram atom of copper, and treating the resulting paste at a temperatureapproidmating 0 C. and in the presence of a small additional amount ofammonia with an alkali-metal hydroxide in amount sumcient for thetheoretical conversionof the aforesaid basic copper salt to copperhydroxide.

3. The method of preparing a cuprammoniumcellulose solution whichcomprises converting a cellulosic material without substantial solutionthereof into a smooth paste by the conjoint action in an aqueous mec'uumoi the constit uents of a basic copper sait containing about 1 gram atomof copper per mol of cellulose and ammonia not exceeding mols per gramatom of copper, and where said basic copper salt ranges in compositionfrom CuX-CM Ol-En to CuX= BCMQH) 2 of the aforesaid basic coppersalt tocopper hydroxide.

l. The method of preparing a cuprammoniumcellulose solution whichcomprises dispersing cellulosic material into a smooth paste in anaqueous medium containing ammonia and the constituents oi a basic coppersalt containin lose, the amount or ammonia not exceeding 6.5

' mols per gramatorn of copper, and treating the said basic copper saltto copper hydroxide.

cellulose solution which comprises converting 5. The method of preparinga cu'prammoniumcellulose solution which comprises dispersing cellulosicmaterial without substantial solution thereof into a smooth paste in anaqueous medium containing ammonia and about 1 gram atom of copper permol of cellulose in the form of the constituents of a basic copper saltranging from CuX-Cu(OH)z to CuX-3Cu('0H)2 where CuX represents a normalcupric salt containing one atom of copper, the amount of ammonia notexceeding 6.5 mols per gram atom of copper, and

treating the resulting paste at a temperature approximating 0 C. withsodium hydroxide in amount suflicient for the theoretical conversion ofthe aforesaid basic copper salt to copper hydroxide.

6. The method of preparing a cuprammoniumcellulose solution whichcomprises dispersing 8- I cellulosic material into a smooth paste in anaqueous medium in the presence of '(1) a basic copper salt within therange of 1 to 3 mols of copperhydroxide permol of normal copper salt and(2) ammonia in amount equivalent to at least 4 mols and not exceeding6.5 mols per gram atom of the total copper in the aforesaid basic coppersalt, and treating the resulting paste at a temperature around C. withan alkali-metal ydroxide in amount sufficient for the theoretical 1conversionof the aforesaid basic copper salt to copper hydroxide andthereby producing a cuprammonium-cellulose solution.

7. The method of preparing a cuprammoniumcellulose solution whichcomprises dispersing cellulosic material into a smooth paste in anhydroxide and thereby producing a cuprammonium-ce llulose solutionsubstantially free from undissolved and partly dissolved fibers and fromundissolved copper salts.

8. The method of preparing a cuprammoniumcellulose solution whichcomprises dispersing cellulosic material into a smooth paste in anaqueous medium containing the constituents per mol of cellulose of (1)about 1 gram atom of copper in the form of a basic copper salt withinthe range of 1 to-3 mols of copper hydroxide per mol of'normal coppersalt and (2) from 4 to 6.5 mols .of ammonia, and dissolving thedispersed cellulosic material to form a cuprammoniumcellulose solutionby'treating said paste at a temperature approximating 0 C. and in thepresence of l to 2 additional mols of ammonia with about 2 mols of addedsodium hydroxide per mol of 1 normal copper salt contained in theaforesaid basic copper salt. 9. The method of preparing acuprammonlumcellulose solution which comprises forming cel-' lulosicmaterial into aslurry with water in the presence of at least one of thechemicalcom- 1 pounds employed in providing the constituents of thebasic copper salt and ammonia hereinafter recited, dispersing thecellulosic material of the resulting slurry without substantial solutionof cellulose into a smooth paste in an aqueous medium in the presence ofthe constituents of (1) a basic copper salt within the range of 1 to 3mols of copper hydroxide per mol of normal substantial solution ofcellulose into a smooth.

monia hereinafter recited, dispersing thecellulosic material of theresulting slurry without paste inan aqueous medium in the presence ofamount sufiicient for the theoretical conversion of the aforesaid basiccopper salt to copper hydroxide and thereby producing a monium-cellulosesolution. 7

11. The method of preparing a cuprammonium-cellulose solution whichcomprises forming a cellulosic material into a slurry with water in thepresence of an alkali-metal hydroxide. dispersing the cellulosicmaterial of the resulting slurry without substantial solution ofcellulose into a smooth paste in an aqueous medium to which a normalcopper 'salt and ammonia are added in such amounts that (1) thealkali-metal hydroxide and the normal copper salt form theoretically abasic copper salt within the range of 1 to 3 mols of copper hydroxideper mol of copper salt and (2) ammonia in amountequiva-V lent to atleast 4 mols per gram atom of the total copper in the aforesaid basiccopper salt, and treating the resulting paste at a temperature around 0C. with an alkali-metal hydroxide in amountsufficient for thetheoretical conver sion of the aforesaid basic copper salt to copperhydroxide and thereby producing a cuprammonium-cellulose solution.

10. The method of preparing a cuprammonium-cellulose solution. whichforming cellulose material into a slurry with water in the presence of.at least one of the chemical compounds employed in providing theconstituents or the basic copper salt and amcomprises Y normal coppersalt and (2). the ammonia is' equivalent to at least 4 mols per mol ofthe added normal copper salt, the aqueous medium containing about 1 gramatom of copper per mol of cellulose, and treating the resulting paste ata temperature around 0 C. with, an alkali-metal hydroxide in amountsufficient with the alkali-'- metal hydroxide initially present for thetheoretical conversion of all the copper present to copper hydroxide andthereby producing a cuprammonium-cellulose solution.

12. The method of preparing a cuprammonium-cellulose solution whichforming a cellulosic-material into a slurry with water in the presenceof sodium hydroxide, dispersing the cellulosic material of the resultingslurry without substantial solution of cellulose into a smooth paste inan aqueous medium containing in addition to said sodium hydroxide suchadded amounts of a normal copper salt and ammonia that (1) the sodiumhydroxide and the normal copper salt form theoretically a basic coppersalt within the range of 1 to 3 mols of copper hydroxide per mol ofnormal copper salt and (2) at least 4 mols of ammonia are present permol of the added normal copper salt, and treating the resulting paste ata temperature approximating 0 C. and in the presence of a smalladditional amount of ammonia with sodium hydroxide in amount sufficientwith" the sodium hydroxide initially present for the theoreticalconversion of all the copperpresent to copper hydroxide and therebyproducing a cuprammonium-cellulose solution.

13. The method of preparing a cuprammoniumcellulose solution whichcomprises forming a cellulosic material into a slurry with water in thepresence of the effective equivalent of a copper tetrammino salt, saidcopper tetrammino salt being present in the amount of about 1 mol permol of cellulose and containing not more than 2.5 mols excess of ammoniaper mol .of salt, dispersing the cellulosic material of the resultingslurry without substantial solution of cellulose into a smooth paste inan aqueousmedium to which an alkali-metal hydroxide is added in cupram-1 comprises such amount that the alkali-metal hydroxide and cient withthe alkali-metal hydroxide previously.

added for the theoretical conversion of all the copper present to copperhydroxide and thereby producing a cuprammonium-cellulose solution.

14. The method of preparing a cuprammoniumccllulose solution whichcomprises forming a cellulosic material into a slurry with water in thepresence of the effective equivalent of a copper tetrammino salt, saidcopper tetrammino salt being present in the amount of about 1 mol permol of cellulose and containing not more than 2.5 mols excess of ammoniaper mol of salt, dispersing the cellulosic material of the resultinslurry without substantial solution of cellulose into a smooth paste inan aqueous medium to which sodium hydroxide is added in such amount umhydroxide previously added for the theoretical conversion of all thecopper present to copper hydroxide and thereby producing a cuprammoni-.um-cellulose solution.

17. The method of preparing a cuprammoniumcellulose solution whichcomprises treating cellulosic material with sodium hydroxide to producea treated cellulose containing from 1.0 to 1.5 mols of sodium hydroxideper mol of cellulose, dispersing the treated cellulose withoutsubstantial solution thereof into a smooth paste in an aqueous mediumcontaining the constituents of a normal copper salt and ammonia, saidnormal copper salt beingpresent in amount such that the copper contentof the paste will be about 1 gram atom of copper'per mol ofcel1u1ose.and

said ammonia being present in the amount of from 4-6.5 mols per gramatom of copper, and treating the resulting paste at a temperatureapproximating 0 C. and in the presence of a small additional amount ofammonia with sodium bythat the sodium hydroxide and the normal coppersalt of said copper tetrammino salt form theoretically a basic coppersalt within the range of 1 to 3 mols of copper hydroxide per mol ofnormal copper salt, and treating the resultin paste at a temperatureapproximating 0 C. and in the presence of a small additional amount ofammonia with sodium hydroxide in amount sufiicient with the sodiumhydroxide previously addedfor the theoretical conversion of all thecopper present to copper hydroxide and thereby producing a cuprammoniumcellulose solution.

15. The method of preparing a cuprammoniumcellulose solution whichcomprises forminga cellulosic material into a slurry with water in thepresence of a normal copper salt, dispersing the cellulosic material ofthe resulting slurry without substantial solution of cellulose into asmooth paste in an aqueous medium to which ammoniaand an alkali-metalhydroxide are added in such amounts that (1) the alkali-metal hydroxideand the normal copper salt form theoretically a basic copper salt Withinthe range of 1 to 3 mols of copper hydroxide per mol of normal coppersalt and (2) the ammonia is equivalent to at least 4 mols per mol ofnormal copper salt present in paste in an aqueous medium to whichammonia and sodium hydroxide are added in such amounts that (1) thesodium hydroxide and the normal droxide in amount suilicient with thatpresent in said treated. cellulose for the theoretical conversion of allthe copper present to copper hydroxide 6.5 mols of ammonia, and treatingthe resulting paste at a temperature approximating 0 C. and

in the presence of a small additional amount of ammonia with sodiumhydroxide in amount sumcient with that present in said treated celluloseto equal about 2 mols per mol of normal copper salt added as aforesaidto the aqueous medium.

19. The method of preparing a cuprammoniumcellulose solution whichcomprises steeping'cellulosic material at a temperature of about 18 C.

in an alkali solution containing about 7.45% of sodium hydroxide,centrifuging the steeped cellulosic material until its sodium hydroxidecontent is from 1 to 1.06 mols per mol of cellulose, dispersing thecentrifuged cellulosic material without substantial solution thereof inan aqueous medium in the presence per mol of cellulose of (1) about 1gram atom of copper inthe form of copper salt form theoretically a basiccopper salt within the range of 1 to 3 mols of copper hydroxide per molof normal copper salt and (2) at least 4 mols of ammonia are present permol of normal copper salt present in said slurry f mi p a basic coppersalt within the range of 1 to. 3 mols of copper hydroxide per mol ofnormal copper salt and (2) from 4 to 6.5 mols of ammonia, and dissolvingthe dispersed cellulosic material to form a cuprammonium-cellulosesolution by treating said paste at a temperature around 0 C. with sodiumhydroxide in amount sufiicient with that present in the aforesaidcentrifuged steeped cellulose for the theoretical conversion of all thecopper present to copper hydroxide.

20. The method of preparing a cuprammoniumcellulose solution whichcomprises steeping cellulosic material in a steeping press at'a tempera-I ture of about 17-19 C. with an alkali solution containing about10l0.3% of sodium hydroxide,

pressing the steeped cellulosic material until its sodium hydroxidecontent is from 1 to 1.06 mols gram atom of copper in the form o! abasic copper salt within the range of 1 to 3 mols of copper hydroxideper mol of normal coppersalt and (2) from 4 to 6.5 mols of ammonia, anddissolving the dispersed celluloslc material toform 9. cu- 5prammonlum-cellulose solution by treating said paste at a'temperaturearound 0 C. with sodium PAUL HENRY SCI-ILOSSER. KENNETH RUSSELL GRAY.

